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From: sck@elsie.UUCP (Steve Kaufman)
Newsgroups: net.misc,net.physics
Subject: Re: perpetual motion
Message-ID: <5079@elsie.UUCP>
Date: Wed, 20-Mar-85 15:28:15 EST
Article-I.D.: elsie.5079
Posted: Wed Mar 20 15:28:15 1985
Date-Received: Sat, 23-Mar-85 02:26:06 EST
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Xref: watmath net.misc:7606 net.physics:2278

> 
> Also, conservation of momentum is a direct consequence of spatial
> translation invariance of the fundamental laws of physics, and
> conservation of energy is a result of time translation invariance.
> 
> The general relativist would point out that the corresponding exact
> physical law (vanishing divergence of stress-energy-momentum tensor)
> shows that the exactly-conserved quantity is not purely physical, and
> the purely physical quantity is not exactly conserved.
>

	Could someone kindly translate the above into English
	for those of us who don't often see phrases like
	"time translation invariance"
		 and
	"vanishing divergence of stress-energy-momentum tensor"?

	Thanks.